Audio Systems: New Yamaha receiver not playing well with Comcast cable box., motorola dct6400, yamaha rx v1700

Question
Bought a new Yamaha RX-V1700 receiver. It's connected via optical cable from receiver to Comcast/Motorola DCT6400 HDDVR cable box.
 Connections are correct and work but with a twist. When I change a channel on the cable box the Yamaha attempts to capture the audio signal, the receiver "locks in" the signal and the sound remains mute.  I can get the sound to pop back on with a movement of any of the buttons on the remote and the sound is perfect.  But, most channels remain mute but pop back to life with a simple touch of a button.  Frustrating to live with.  Seems that my Yamaha is not playing well with Comcast...or visa versa.  Any thoughts would be appreciated.
Thanks  Steve

Answer
Hi Steve,

Sorry to take so long to get a response back to you, this is a head scratcher.

I don't often work with consumer audio in my professional life, but this particular receiver is one I have used extensively even in the industrial realm, and I have never come across this as a punch-list item.

Scanning the manual I have on file I do not see this particular issue on the trouble-shooting tree either.

I can only guess at one of two options:

1) control programming error:
Do you have a touch-screen (Crestron, AMX, Xantech, etc.) or similar third-party remote control (Philip's Pronto, etc.) you're using to operate your system?  If so, the control programming may have an error (especially if it's operating through the RS-232 port) that is not switching audio over with video or otherwise causing fault.

2) Accidental "intentional setting"
you may have accidentally made some user-setting that leaves this behavior as a consequence.  The classic example would be "Audio Breakaway" on the video switching, which would require two selection to be made - the video source you want to view and the audio source you want to listen to.

3) Faulty sync or control board.
You may have some part of your electronic connection between the cable box and the Yamaha that is not to spec, and the ability of your Yamaha to perform seamlessly is hindered for it.
Knowing Yamaha's track record at this level of performance, I do tend to suspect either the cable box or the co-ax/optical connection between the two.  I would first replace the cable or try some other method of connection (i.e., if you're using optical, go to co-ax - or vice-versa)
Next try to get a replacement cable box.  It is entirely possible that the signal is either too weak or distorted to easily "lock" in with the Yamaha.
Next I would get a service ticket/RMA for the Yamaha.
-You might want to step on it to make warranty/return deadlines.

I wish you luck!